style: update border-radius and padding values across components

- standardize border-radius from 8px to 6px for consistent styling
- adjust padding values from 1rem to 0.75rem for better visual hierarchy
- remove redundant overflow-y properties for cleaner code

docs/.vitepress/theme/components/appendix/database-intro/DatabaseEvolutionDemo.vue

@@ -113,10 +113,10 @@ const currentStage = computed(() => {
 <style scoped>
 .data-evolution-demo {
   border: 1px solid var(--vp-c-divider);
-  border-radius: 8px;
+  border-radius: 6px;
   background: var(--vp-c-bg-soft);
-  padding: 1rem;
-  margin: 1rem 0;
+  padding: 0.75rem;
+  margin: 0.5rem 0;
 }
 
 .demo-header {
@@ -163,7 +163,7 @@ const currentStage = computed(() => {
   position: relative;
   cursor: pointer;
   padding: 0.5rem;
-  border-radius: 8px;
+  border-radius: 6px;
   transition: all 0.2s ease;
 }
 
@@ -178,7 +178,7 @@ const currentStage = computed(() => {
 .stage-icon {
   width: 40px;
   height: 40px;
-  border-radius: 8px;
+  border-radius: 6px;
   background: var(--vp-c-brand);
   display: flex;
   align-items: center;
@@ -231,8 +231,8 @@ const currentStage = computed(() => {
 
 .stage-detail {
   background: var(--vp-c-bg);
-  border-radius: 8px;
-  padding: 1rem;
+  border-radius: 6px;
+  padding: 0.75rem;
   margin-top: 0.75rem;
   border: 1px solid var(--vp-c-divider);
 }