SELECT 
  cscart_bm_layouts.* 
FROM 
  cscart_bm_layouts 
WHERE 
  1 
  AND is_default = 1 
  AND theme_name = 'bright_theme' 
  AND storefront_id = 1

Query time 0.00021

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_bm_layouts system is_default 1

Result

layout_id name is_default width layout_width min_width max_width theme_name style_id storefront_id
1 Main 1 16 fluid 280 1200 bright_theme Bright_theme 1