Microsoft account sign in isn't properly dark themed so it flashes black to white repeatedly -- giving me a headache

### Description

I use the dark theme (to avoid the brightness of the light theme) but the Microsoft account sign in UI is not properly dark themed so it flashes a bright white image many times a day giving me a headache. See the screenshots. The secondary bug is that I have to repeatedly sign in multiple times a day instead of it being saved: https://github.com/microsoft/vscode/issues/316881. This is when signing in for the Azure DevOps MCP server.

### Issue Details

Item|Value
---|---
Issue Category|Bug
Target|Visual Studio Code - Insiders
VS Code Version|Code - Insiders 1.134.0-insider (0f3c3b53028901b912211a99b23232b76017bcfc, 2026-08-13T18:02:30Z)
OS Version|Windows_NT x64 10.0.26200

System Info

Item|Value
---|---
VS Code Version|Code - Insiders 1.134.0-insider (0f3c3b53028901b912211a99b23232b76017bcfc, 2026-08-13T18:02:30Z)
OS Version|Windows_NT x64 10.0.26200
CPUs|AMD EPYC 7763 64-Core Processor (32 x 2445)
GPU Status|2d_canvas: unavailable_software
GPU0: VENDOR= 0x1414, DEVICE=0x008c [Microsoft Basic Render Driver], DRIVER_VENDOR=Microsoft, DRIVER_VERSION=10.0.26100.8875 *ACTIVE*
GPU1: VENDOR= 0x1414, DEVICE=0x008c [Microsoft Basic Render Driver], DRIVER_VERSION=10.0.26100.8875
GPU2: VENDOR= 0x1414, DEVICE=0x008c [Microsoft Basic Render Driver], DRIVER_VERSION=10.0.26100.8875
Machine model name:
Machine model version:
direct_rendering_display_compositor: disabled_off_ok
gpu_compositing: disabled_software
multiple_raster_threads: enabled_on
opengl: disabled_off
rasterization: disabled_software
raw_draw: disabled_off_ok
skia_graphite: disabled_off
trees_in_viz: disabled_off
video_decode: disabled_software
video_encode: disabled_software
webgl: unavailable_software
webgpu: unavailable_software
webnn: unavailable_software
Load (avg)|
Memory (System)|127.95GB (47.47GB free)
Process Argv|--crash-reporter-id a69cc171-5b51-40e5-8ee2-86a28162322c
Screen Reader|no
VM|0%
Remote|WSL: Ubuntu-26.04
Remote OS|Linux x64 6.18.33.2-microsoft-standard-WSL2
Remote CPUs|AMD EPYC 7763 64-Core Processor (32 x 0)
Remote Memory (System)|94.29GB (75.45GB free)
Remote VM|0%
Remote|WSL: Ubuntu-26.04
Remote OS|Linux x64 6.18.33.2-microsoft-standard-WSL2
Remote CPUs|AMD EPYC 7763 64-Core Processor (32 x 0)
Remote Memory (System)|94.29GB (75.32GB free)
Remote VM|0%
User Agent|Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Code-Insiders/1.134.0-insider Chrome/148.0.7778.280 Electron/42.8.1 Safari/537.36
Installation pure|true

A/B Experiments

```
vsliv368:30146709
pythonvspyt551cf:31249598
nativeloc1:31118317
dwcopilot:31158714
471b6256:31240254
dwoutputs:31242946
copilot_t_ci:31333650
g012b348:31231168
pythonrdcb7:31268811
pythonpcpt1cf:31399617
6518g693:31302842
envsactivate1:31349248
editstats-enabled:31346256
cloudbuttont:31366566
3efgi100_wstrepl:31403338
gpt-41-copilot-3x:31561746
metis_rerank_treatment1:31411021
cp_cls_t_966_ss:31526232
4je02754:31455664
c3h7c220:31478652
ge8j1254_inline_auto_hint_haiku:31490507
cp_cls_c_1081:31454833
conptydll_true:31485575
e9c30283:31453065
test_treatment2:31471001
c9b86496:31447327
capico_a_098a3278:31555650
ei9d7968:31462942
nes-extended-on:31455475
de16b994:31458079
89g7j272:31506658
hhf17803:31462392
i2gc6536:31472020
52612955:31508042
h08i8180_copy:31475366
ddid_t:31478204
hmra_i5g22:-9
bjc72774_agent_sandbox:31538428
7df3h592:31491241
cp_cls_t_1082:31535311
logging_enabled_new:31490725
jb_cp_cls_t_632:31543129
b1g4i769:31503653
ha629193:31508444
cdk-lw-on:31524445
a1ije391_t:31533808
jbcp_cls_pctr_t:31531130
3f904173:31522231
cp_intellij_t_nes:31548657
d7b18187:31526828
hide-eh-duplicates:31543293
replace-eh-with-ah:31545853
ihg5j128:31534457
f412h606:31543414
69d46680:31554865
90g4a790:31550158
enable_editor_pane_layout:31551200
52258b4d:31547953
36h42362:31560305
c7c27ce7:31551212
voicemodeon:31566386
a81hg326:31551415
6577i413_copy:31558653
1h923230:31564177
0dg73464:31554309
gpt56sol_default:31557178
treatment-23-1:31555779
unuse_dynamic_mcp:31555281
0c1h4866:31562347
vrbsty_fls:31561057
4553j735_t_off:31561845
be7id924_c:31561848
plus-and-new:31566205
5b8j3302:31564600
mangle-name-treatment:31565185
permission_prompt_treatment:1294978
ccr_pr_nudge_control:1319470
```

It flashes black -> white -> black -> white -> black